Hit me with your best shot: combining gene editing events to deliver iron and zinc biofortified rice.

Micronutrient deficiencies, particularly of iron (Fe) and zinc (Zn), are major global health concerns for humans, especially in populations that rely heavily on cereal-based diets. Rice grains, one of the world's most consumed staple crops, have low concentrations of bioavailable Fe and Zn, especially in the endosperm which constitutes white rice, the most consumed rice. Biofortification is proposed as an excellent cost-effective strategy to solve the problem. Recent advances in CRISPR-based genome editing now allow precise manipulation of genes controlling mineral uptake, transport, sequestration, and grain partitioning, offering new opportunities to generate non-transgenic, biofortified crop. Here we discuss current knowledge on the genetic control of Fe and Zn accumulation in rice grains and evaluate how this information can be leveraged to design effective genome editing strategies for nutritional improvement. We focus on candidate genes involved in vacuolar sequestration, metal chelator biosynthesis and transport, plasma membrane transport, regulatory pathways controlling metal homeostasis, and phytic acid metabolism affecting mineral bioavailability. Evidence from loss-of-function mutants, promoter engineering, natural allelic variation, and precise sequence editing demonstrates that targeted manipulation of these pathways can substantially enhance Fe and Zn accumulation, particularly in polished rice, without major yield penalty. We further propose potential multiplex gene editing approaches to combine alleles and optimize metal allocation to the endosperm. These advances provide a framework for the rational development of next-generation, non-transgenic biofortified rice cultivars.